Spinal cord stimulation systems and other stimulation devices frequently utilize an implantable pulse generator (IPG) for treating chronic pain by delivering electrical stimulation pulses from an electrode array placed epidurally near a patient's spine. Spinal cord stimulation (SCS) is a well-accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an IPG and at least one stimulating lead having one or more electrode contacts (an electrode array) connected to the lead.
Electrical pulses may be delivered to the dorsal column fibers within the spinal cord through the electrode contacts which are implanted along the dura of the spinal cord. In a typical situation, the attached stimulation lead exit the spinal cord and are tunneled around the torso of the patient to a sub-cutaneous pocket where the pulse generator may be implanted.
In order to protect the electronic circuitry from environmental conditions and/or other damage while the IPG is implanted within a patient, the IPG is frequently enclosed in a hermetic, titanium case to provide protection from the body environment. Traditionally, the titanium case includes two halves. Recesses are formed in each of the halves such that when the two halves are coupled together, holes are formed. Feedthrus extend through these holes to the outside, which feedthrus are electrically coupled to the electronic circuitry located within the IPG.
In particular, to properly establish the feedthrus, the titanium halves often must be aligned with respect to each other and with respect to the feedthru. Once aligned, the assembly is welded and checked for leaks. If the resulting assembly is not hermetically sealed, the assembly is reworked. Even if the assembly is sealed during formation, it may be possible for the titanium case to leak where it interfaces with the feedthrus. If the titanium case does leak, resulting in the ingress of moisture, the IPG may fail prematurely due to damage of the electronic circuit within the IPG.
Further, some designs allow the battery that powers the IPG to be recharged through an inductive coupling using an external power source. The use of a titanium case may partly shield the power transmission and limit the rate at which the battery may be charged. More specifically, eddy currents may be generated within the titanium case during inductive power transmission. The production of eddy currents reduces the efficiency of power transmission and can cause the titanium case to heat up to an undesirably hot temperature.